It’s September of 1960, and John F. Kennedy is locked in a dead heat for the White House. Although his opponents in the primary have criticized him for his youth and history of illness, Kennedy’s biggest liability in the general election is something else: his religion. In Protestant churches across the country, ministers are questioning the motivations and allegiance of a Catholic politician, and Kennedy has decided to face their accusations directly. In a speech to the Greater Houston Ministerial Association, he defends his faith, promising to use only his conscience to make decisions in the national interest, not the counsel of Catholic leaders like the Pope.

But when he got to the Oval Office, everything would change. During a discussion of PBS’s new documentary, JFK, hosted in part by The Atlantic, historian Timothy Naftali speculated that John was not the most overtly devout Kennedy brother.

John Kennedy's mother, Rose, in 1954. (AP Photos)

“President Kennedy, as I understand it, was a man of compartments,” he said. “In the Oval Office conversations, I’ve never—never!—heard him refer to faith or God. But that was business—I’m not sure what would happen when he was home or with his family. I suspect his mother would expect him to talk about Catholicism.”

Robert Kennedy, who ran his brother’s campaign for president, was more openly religious. “I don’t think every member of the Kennedy family was equally devout,” Naftali said. “My sense from the literature is that Robert Kennedy was devoutly Catholic and that you would have heard him mention Catholicism, unlike his brother.”

Perhaps he was better able to afford the luxury of speaking openly about his faith than his brother. John Seigenthaler, a longtime journalist who served as one of Robert Kennedy’s political advisers, recalled the intense vitriol John Kennedy faced because of his religion. “There was a cadre of anti-Catholics that were absolutely determined that on that basis he was going to be defeated,” Seigenthaler said.

This brand of discrimination seems unthinkable in today’s political world, especially considering that five of the current Supreme Court Justices are Catholic. That level of Catholic leadership in government "would be unbelievable during that campaign. The literature that was circulated across this country during that campaign was disgusting, sickening,” Seigenthaler said.

Kennedy’s father was also frustrated by what he saw as a lack of support from the Catholic community. “The old dad, Joseph Kennedy, said to Jackie, ‘John can’t leave the Catholic Church, but I might,’” Naftali said. “He was so angry at how people who had been supportive financially for a long time didn’t support his son in the election.”

As Election Day approached, Kennedy decided to take a chance on persuading Protestants that he could represent them with integrity. At the end of his famous speech in Houston, he answered questions on dogma from the ministers in the audience. “A Protestant minister stood and had what I’m sure was a Catholic encyclopedia,” Seigenthaler recalled. “He read an excerpt from it that had to do with some edict defined as ‘mental reservation.’ You were led to believe that it was part of the Catholic faith to lie and make a ‘mental reservation’ to God. So this minister said [to Kennedy], ‘I’d like to know your response—this is from a Catholic encyclopedia, it is dogma, it is faith, and I’d like to know what you have to say about it.’”

In that moment, Kennedy didn’t hesitate to choose politics over papacy. “His answer is, ‘I never heard it, no one in my life has ever said to me anything about mental reservation, and furthermore, I reject it,’” Seigenthaler said. “I don’t know whether the Pope belched.”